A phenomenon where people with little knowledge or skill think they know more or have more skill than they do. This occurs while simultaneously overlooking and/or underestimating the knowledge and skills of those involved in the task at hand.

The Cooker: "Why does the Old Man always tell us how to live our lives?"
Pete Dick: "I believe he is suffering from the Dunning-Kruger effect."

When someone is bad/stupid/ignorant in a field, and thinks they are great/good/guru/expert. This normally happens due to people not having enough knowledge in that field to even know that they are bad at this field. A great place to find and report these people is at /r/iamverysmart

Dude1 : I am an expert in math
Dude2 : You are falling to the dunning-kruger effect (seriously wtf why do I have to include the word in this), all you know is how to add and subtract

A condition where a person so dumb, that he fails to realise how dumb he actually is. Frankly, lacking the competence to identify incompetence - often resulting is immense self-confidence and talking massive cock.

In common usage, it means "clueless of being ignorant" but it's used to add an air of fake scientific authority to a cheap shot. It generally outs the author as an incompetent writer, ironically exhibiting the Dunning-Kruger effect themselves.